1. Field of the Invention
The Present invention relates to a lightning detector and, more specifically, to a lightning detector by utilizing the characteristics of a coherer equipped with a decoherer
2. Description of the Related Art
There have heretofore been put into practice or proposed a variety of lightning detectors which can roughly be classified into (1) those without using a coherer and (2) those using a coherer.
Some devices pertaining to (1) uses {circle around (1)} a lightning wire of, for example, a high-tension transmission line. In this case, however, the detector line (lightning wire) inevitably becomes lengthy for maintaining a precision for detecting the potential relative to ground, and the detector line itself is subject to be destroyed by a thunder-bolt.
There has further been proposed a method or a device {circle around (2)} which confirms the presence of a thundercloud based upon the data from a so-called meteorological radar (cloud radar) to estimate the degree of danger accompanied thereby. However, the device becomes expensive though the reliability is not so high. Concerning the method or the device {circle around (2)}, it has been attempted to render an overall judgement by taking into consideration the data obtained from artificial satellites and telemeter-measured values of precipitation without, however, satisfactory results.
Further, {circle around (3)} a device, SKYSCAN ((trademark)), taught in U.S. Pat. No. 5,541,501 has been placed in the market in the U.S.A. and in other countries. This is a lightning detector which displays the distance from the lightning position by comparing and analyzing the frequency and intensity of electromagnetic waves due to lightning.
As the manual of the product states xe2x80x9cBE AWARE THAT STORMS CAN FORM DIRECTLY OVER YOUR LOCATION, OFFERING LITTLE OR NO ADVANCE WARNING EVEN WHEN USING A SKYSCANxe2x80x9d, however, this device is not capable of detecting lightning just overhead, and it Lust be said that its reliability is very low.
The method or the device (2) was developed based on the re-discovery that the coherer sharply reacts to a change in the intensity of the electromagnetic field inclusive of the static electric field, and there have been proposed many variations as taught in, for example, {circle around (4)} Japanese Unexamined Patent Publication (Kokai) No. 50154/1996, {circle around (4)} Japanese Unexamined Patent Publication (Kokai) No. 180911/1997 and {circle around (5)} U.S. Pat. No. 5,399,962. However, the device of the publication {circle around (4)} is often affected by alternating electric field noise from, for example, a high-tension transmission line, by the modulated carrier waves of broadcast or communication and, particularly, by PWM (pulse width modulated) intermittent wave noises, and, hence, malfunctions, accounting for a major cause of inhibiting the widespread use as the lightning detector with coherer.
The device of the publication {circle around (5)} is a highly sensitive coherer having a low self-operation voltage (threshold voltage), which is very effective in detecting a very weak spark discharge. This device, however, is rather cumbersome to use for the spontaneous aerial discharge of large electric power such as of thunder discharge (lightning). This device has not been proposed for detecting lightning and, besides, involves a problem in practice.
The device of the publication {circle around (6)} is a surge protector for a high-tension transmission line and uses a coherer. This device detects damped wave disturbances but is not designed for detecting lightning. The damped wave disturbances are caused by spark discharge due to a thunder-bolt or a short-circuit (abnormal discharge inclusive of arc discharge or corona discharge caused by salt damage). The device of the publication {circle around (6)} has been designed for detecting abnormal conditions on the high-tension lines.
That is, the coherer has wide frequency characteristics and exhibits a considerable degree of sensitivity even for artificial spark discharge noise. The frequency spectrum of artificial spark discharge noise exists chiefly in a high-frequency region of about 1 Mhz or higher. On the other hand, the electromagnetic waves of lightning discharge have low frequencies in the regions of from VLF to MF. According to the prior art, the frequencies could not be distinguished. Since high-frequency noises were easily picked up, the sensitivity to the electromagnetic waves of lightning became relatively low.
With the conventional techniques {circle around (1)} to {circle around (3)} and {circle around (4)} to {circle around (6)}, it is difficult to reliably detect the intensity of the electromagnetic waves of not smaller than a predetermined value caused by thunder-bolt.
There has not yet been known a lightning detector equipped with a lightning circuit for protecting itself and with a coherer, capable of detecting thunder that is approaching or is separating way.
The present inventors, therefore, have accomplished a lightning detector capable of more correctly detecting lightning by incorporating a lightning circuit having a low-pass filter (hereinafter often abbreviated as LPF or is often called xe2x80x9cfilter transformerxe2x80x9d) and/or an aerial discharge gap between the antenna and the coherer, to offer the function of detecting thunder that is approaching or is separating away.
It is therefore an object of the present invention to provide a lightning detector which is capable of reliably predicting lightning free from the danger of being struck by lightning by using a relatively simply constructed coherer with a decoherer.
Another object of the present invention is to alert the degree of danger of lightning by using an indicator by detecting and storing lightning data and thunder data of a plurality of thunder-bolts at a distance, and by comparing at least two pairs of these data.
A further object of the present invention is to produce an indication/alarm by statically detecting the fact that the lightning detector is approaching the lightning range and/or by dynamically detecting whether the thunder-bolt is approaching/moving away.
The invention provides a lightning detector comprising an antenna, a coherer with a decoherer, a low-pass filter installed between the antenna and the coherer, an indicator and a power source, the lightning detector detecting the intensity of impulse electromagnetic waves of not smaller than a predetermined value produced by a thunder-bolt outside the lightning range, and producing an indication and/or an alarm on an indicator to tell that the detector is approaching the lightning range.
The invention provides a lightning detector as met forth above 1, wherein the coherer comprises one filled with metal particles or metal particles coated with an oxide film between a pair of electrodes in an insulating tube that is sealed, and the decoherer comprises one that gives mechanical vibration to the coherer from the external side.
The invention provides a lightning detector as set forth above, wherein the coherer is equipped with a lightning circuit capable of adjusting the aerial discharge gap.
The invention provides a lightning detector as set forth above, wherein the lightning circuit is equipped with an exclusive coherer (coherer No. 2) for the lightning circuit, separate from the coherer (coherer No. 1) for the alarm.
The invention further provides a lightning detector as set forth above, wherein a plurality of thunderbolts stronger than a predetermined level are measured and recorded as electromagnetic wave intensity difference xcex94En and sound pressure difference xcex94Pn, the moments of inputs of these signals are stored in a storage medium in time series, a red lamp is turned on when a gradient of time difference xcex94Tn of xcex94En and xcex94Pn of when a pair of electric signal and sound signal are input, is (xe2x88x92) over a time of at least m pairs (m is a positive integer), a yellow lamp is turned on when the gradient of time difference xcex94Tn is close to (0) and a green lamp is turned on when the gradient of time difference xcex94Tn is (+), to indicate the danger of a thunder-bolt.
The invention will now be described in detail.
Lightning emits electromagnetic waves of countless frequencies which are distributed in a relatively low range (VLF to MF bands).
The field intensities of the electromagnetic waves of these frequencies can be detected in a synthesized form. Since the intensities of electromagnetic fields of various frequencies sharply change with the passage of time, the intensity of the electromagnetic field that is detected usually changes sharply.
It has been known that in a typical lightning discharge, the intensity of the electromagnetic field changes as much as 120 V/m at the greatest 100 xcexcS as measured at a point 20 Km away from the point where the discharge is taking place (as calculated from a maximum waveform of main discharge, H. Norinder, Handbook of Wireless Engineering, 10, Chapter 6, 10-69, FIG. 10-94: Lightning Discharge waveform, Ohm Co., May 25, 1964).
Such a sharp and large change in the intensity of the electromagnetic field is unthinkable in the artificial electromagnetic waves that are used in the daily broadcasts and communications. In fact, however, the coherer reacts to a sharp and large change in the electric field intensity. In fact, a coherer that was fabricated for testing favorably reacted to a change in the field intensity of 60 V/m in 100 xcexcS (in an electric field due to artificial spark discharge).
The coherer, in contrast, is very insensitive and does not react to electromagnetic waves of a predetermined field intensity that is accompanied by a mild change in the electromagnetic field intensity. It was confirmed that the coherer fabricated for testing did not react even under a predetermined electromagnetic field of 10 V/m (such an electromagnetic field intensity is very larger than those that are usually used).
The present inventors have re-discovered such characteristic properties of the coherer, and have applied such properties to the lightning detector and have further added some contrivances.
In the coherer fabricated for testing, a mixture powder of Ni and Ag (95% by weight of Ni, 5% by weight of Ag, the particles having an average diameter of about 100 to 1500 xcexcm) was sandwiched by Ag electrodes, and was sealed in a glass tube together with the dry air.
The coherer comprises particles of a single metal such as Ni, Co, Fe, Mn, Zn, Cu, Ag, Au, Pd, Al or Pt or mixture particles thereof that are filled in a fluidizing manner in an insulating tube such as of ebonite, glass or plastic, and a pair of electrodes are provided at both ends of the insulating tube. Usually, the surfaces of these metal particles are covered with an oxide film having a low electrically conducting property. Therefore, the contact resistance is so large that no current flows across both terminals.
In the case of a stable metal such as Au or Pt, the effect of the oxide film is small and a generally good electrically conducting property is exhibited. Therefore, the initial insulating property is maintained due to gaps among the particles and the lowly electrically conducting substance such as silicone oil that is added. When an impulse voltage due to lightning is applied across both terminals, the metal particles in the coherer are destroyed for their insulation and are cohered to conduct the electricity.
The decoherer is a device for recovering the insulating property of the coherer that is cohered. In its most primitive form, the glass tube is hit by hand using a wood hammer or a plastic hammer. This, however, may be automatically carried out by mechanically vibrating the glass tube relying upon ultrasonic waves (20 KHz or higher) generated by a piezo-electric element or an electromagnet after every predetermined period of time.
The dynamic detector means accomplishes dynamic detection only independently of the static detection, and could become an effective lightning detector means for indicating danger (see embodiment 4). That is, there exists an invention in the dynamic detector means itself.
Concerning other respects, the invention will be described in further detail with reference to the embodiments below.